Perturbation theory for evolution of cooperation on networks

Network structure is a mechanism for promoting cooperation in social dilemma games. In the present study, we explore graph surgery, i.e., to slightly perturb the given network, towards a network that better fosters cooperation. To this end, we develop a perturbation theory to assess the change in the propensity of cooperation when we add or remove a single edge to/from the given network. Our perturbation theory is for a previously proposed random-walk-based theory that provides the threshold benefit-to-cost ratio, $(b/c)^*$, which is the value of the benefit-to-cost ratio in the donation game above which the cooperator is more likely to fixate than in a control case, for any finite networks. We find that $(b/c)^*$ decreases when we remove a single edge in a majority of cases and that our perturbation theory captures at a reasonable accuracy which edge removal makes $(b/c)^*$ small to facilitate cooperation. In contrast, $(b/c)^*$ tends to increase when we add an edge, and the perturbation theory is not good at predicting the edge addition that changes $(b/c)^*$ by a large amount. Our perturbation theory significantly reduces the computational complexity for calculating the outcome of graph surgery.Comment: 31 pages, 6 figure

Recasting the cancer stem cell hypothesis: Unification using a continuum model of microenvironmental forces

Purpose of review Here, we identify shortcomings of standard compartment-based mathematical models of cancer stem-cells, and propose a continuous formalism which includes the tumor microenvironment. Recent findings Stem-cell models of tumor growth have provided explanations for various phenomena in oncology including, metastasis, drug- and radio-resistance, and functional heterogeneity in the face of genetic homogeneity. While some of the newer models allow for plasticity, or de-differentiation, there is no consensus on the mechanisms driving this. Recent experimental evidence suggests that tumor microenvironment factors like hypoxia, acidosis, and nutrient deprivation have causative roles. Summary To settle the dissonance between the mounting experimental evidence surrounding the effects of the microenvironment on tumor stemness, we propose a continuous mathematical model where we model microenvironmental perturbations like forces, which then shape the distribution of stemness within the tumor. We propose methods by which to systematically measure and characterize these forces, and show results of a simple experiment which support our claims

Free Negroes - The Development of Early English Jamaica and the Birth of Jamaican Maroon Consciousness, 1655-1670

The English conquest of Jamaica in 1655 was a turning point in the history of Atlantic World colonialism. Conquest displaced the Spanish colony and its subjects, some of who fled into the mountainous interior of Jamaica and assumed lives in isolation. This project reconstructs the historical experiences of the “negro” populations of Spanish and English Jamaica, which included its “free black”, “mulattoes”, indigenous peoples, and others, and examines how English cosmopolitanism and distinct interactions laid the groundwork for and informed the syncretic identities and communities that emerged decades later. Upon the framework of English conquest within the West Indies, I explore the experiences of one such settlement alongside the early English colony of Jamaica to understand how a formal relationship materialized between the entities and how its course inflected the distinct socio-political identity and emergent political agency embodied by the Jamaican Maroons. To this end, this study reconceptualizes the social and political foundations of the “negroes” who became the Jamaican Maroons removed from the teleology of the Maroon Wars and its resultant Treaty of 1738-1739

Central governance based on monitoring and reporting solves the collective-risk social dilemma

Monitoring and reporting incorrect acts are pervasive for maintaining human cooperation, but in theory it is unclear how they influence each other. To explore their possible interactions we consider spatially structured population where individuals face the collective-risk social dilemma. In our minimal model cooperator players report defection according to the loss of their interests. In parallel we assume a monitoring institution that monitors all group member and identifies wrong behavior with a certain probability. In response to these feedbacks a sanctioning institution develops punishment schemes by imposing fines on related defector players stochastically. By means of Monte Carlo simulations, we find that the introduction of monitoring and reporting mechanisms can greatly promote the evolution of cooperation and there exists a sudden change of the cooperation level by varying model parameters, which can lead to an outbreak of cooperation for solving the collective-risk social dilemma.Comment: 6 figure

Speciation dynamics of an agent-based evolution model in phenotype space

This dissertation is an exploration of phase transition behavior and clustering of populations of organisms in an agent-based model of evolutionary dynamics. The agents in the model are organisms, described as branching-coalescing random walkers, which are characterized by their coordinates in a two-dimensional phenotype space. Neutral evolutionary conditions are assumed, such that no organism has a fitness advantage regardless of its phenotype location. Lineages of organisms evolve by limiting the maximum possible offspring distance from their parent(s) (mutability, which is the only heritable trait) along each coordinate in phenotype space. As mutability is varied, a non-equilibrium phase transition is shown to occur for populations reproducing by assortative mating and asexual fission. Furthermore, mutability is also shown to change the clustering behavior of populations. Random mating is shown to destroy both phase transition behavior and clustering. The phase transition behavior is characterized in the asexual fission case. By demonstrating that the populations near criticality collapse to universal scaling functions with appropriate critical exponents, this case is shown to belong to the directed percolation universality class. Finally, lineage behavior is explored for both organisms and clusters. The lineage lifetimes of the initial population of organisms are found to have a power-law probability density which scales with the correlation length exponent near critical mutability. The cluster centroid step-sizes obey a probability density function that is bimodal for all mutability values, and the average displays a linear dependence upon mutability in the supercritical range. Cluster lineage tree structures are shown to have Kingman\u27s coalescent universal tree structure at the directed percolation phase transition despite more complicated lineage structures. --Abstract, page iii

Fatal attraction: a critique of Carl Schmitt's international political and legal theory

The ongoing Schmitt revival has extended Carl Schmitt's reach over the fields of international legal and political theory. Neo-Schmittians suggest that his international thought provides a new reading of the history of international law and order, which validates the explanatory power of his theoretical premises – the concept of the political, political decisionism, and concrete-order-thinking. Against this background, this article mounts a systematic reappraisal of Schmitt's international thought in a historical perspective. The argument is that his work requires re-contextualization as the intellectual product of an ultra-intense moment in Schmitt's friend/enemy distinction. It inscribed Hitler's ‘spatial revolution’ into a full-scale reinterpretation of Europe's geopolitical history, grounded in land appropriations, which legitimized Nazi Germany's wars of conquest. Consequently, Schmitt's elevation of the early modern nomos as the model for civilized warfare – the ‘golden age’ of international law – against which American legal universalism can be portrayed as degenerated, is conceptually and empirically flawed. Schmitt devised a politically motivated set of theoretical premises to provide a historical counter-narrative against liberal normativism, which generated defective history. The reconstruction of this history reveals the explanatory limits of his theoretical vocabulary – friend/enemy binary, sovereignty-as-exception, nomos/universalism – for past and present analytical purposes. Schmitt's defective analytics and problematic history compromise the standing of his work for purposes of international theory